DESCRIPTION: Preliminary data indicate that the rate of oleic acid oxidation is 21 percent increased compared to palmitic acid. If the ratio of OA to PA in the diet were to increase, the rate of total fatty acid oxidation in the fed state also may increase; thus, daily fat balance might be decreased in humans fed diets enriched in OA. This would have significance to the treatment and prevention of obesity. Indirect calorimetry will be performed in the fed and fasting state in 34 young, healthy adults who will be studied under two conditions: after a 30-day, solid food diet ("run-in phase") and again, after a 30-day formula diet. The subjects will be randomized to receive either a Control Formula similar to the solid food diet (OA=PA=16.4 percent total kcal) or a High Oleic Acid Formula (OA=31.4 percent kcal; PA=1.7 percent kcal). Using dual-energy x-ray absorptiometry, body composition will be monitored before and after the formula diet. The principal investigator (PI) will address four specific aims. In specific aim 1, the PI will determine if a higher intake of oleic acid (and a reciprocally lower intake of palmitic acid) is associated with a higher rate of fat oxidation. The PI hypothesizes that the rate of fat oxidation (g/hr) in the fed state, adjusted for the covariate effect of the rate of fat oxidation on the solid food diet, will be higher (30 percent) in those subjects randomized to the OA-enriched diet compared to controls. In the specific aim 2, the PI will measure energy intake required to maintain constant body weight during each diet and to measure fat-free mass and fat mass, before and after each dietary change. The PI hypothesizes that a higher rate of fat oxidation on the high OA diet will be associated with a higher energy intake required to maintain constant body weight. In specific aim 3, the PI will compare fat oxidation on the liquid formula diet with that observed on the solid food diet. The PI hypothesizes that fat oxidation will increase in those fed the OA-enriched diet. In specific aim 4, the PI will measure the thermic effect of feeding during both the solid food and formula diet periods. The PI hypothesizes that the high OA feeding will be associated with a higher thermic effect of feeding.